Outside the Guildhall in Kingston, some ostentatious blue railings are doing a good job of protecting what could be any old piece of rock. This two-foot tall grey slab, sat on a plinth, divides opinion as to its historical significance.

Over the centuries, the stone has been a block for riders to mount their horses, a piece of a long-lost chapel, and, possibly, played a crucial part in the creation of England.

The decoration comes from the fact that Kingston once hosted royalty. Between two to seven Saxon kings are thought to have had their coronations here during the 900s. However, it wasn’t until almost a millennium later that the Victorians became convinced that this ‘coronation stone’ was used as a royal seat, hence its ornate memorial.

Nobody really knows for sure whether the stone was used for the ceremonies. However, more interesting is the reason Kingston was chosen as the location. During Saxon times, England was divided into multiple kingdoms and the River Thames at Kingston marked the border for two of them, Wessex and Mercia. One Saxon king, Athelstan, had ambitions to unite England under a single kingdom and probably chose to have his coronation at Kingston for its geographical symbolism. Crowned here in 925, he then went on to conquer Northumbria and become the first legitimate King of England.

So what about the stone? Even if its royal associations are not proven, the rock probably has a dramatic story all its own. Like Stonehenge, it is made of sarsen, a rock type that is rarely found this close to London. One theory is that it was flushed here by glacial meltwaters at the end of the last ice age 12,000 years ago. Otherwise, it could have been transported to Kingston from the South Downs coastal region where the rock is more common.

Because sarsen is made from the compression of sand and mud over millions of years, it is extremely durable – the coronation stone is thought to be between 40 and 66 million-years-old. Perhaps such an old and unique piece of rock deserves its decoration, regardless of kingly use.